The error logs in whonix-ws-16 were like this:
Ign:1 tor+https://fasttrack.debian.net/debian bullseye-fasttrack InRelease
Ign:2 tor+https://deb.whonix.org bullseye InRelease
Ign:3 https://deb.qubes-os.org/r4.2/vm bullseye InRelease
Ign:4 tor+https://deb.debian.org/debian bullseye InRelease
Ign:5 tor+https://deb.kicksecure.com bullseye InRelease
Ign:1 tor+https://fasttrack.debian.net/debian bullseye-fasttrack InRelease
Ign:2 tor+https://deb.whonix.org bullseye InRelease
Ign:3 https://deb.qubes-os.org/r4.2/vm bullseye InRelease
Ign:6 tor+https://deb.debian.org/debian bullseye-updates InRelease
Ign:5 tor+https://deb.kicksecure.com bullseye InRelease
Ign:1 tor+https://fasttrack.debian.net/debian bullseye-fasttrack InRelease
Ign:2 tor+https://deb.whonix.org bullseye InRelease
Ign:3 https://deb.qubes-os.org/r4.2/vm bullseye InRelease
Ign:7 tor+https://deb.debian.org/debian-security bullseye-security InRelease
Ign:5 tor+https://deb.kicksecure.com bullseye InRelease
Err:1 tor+https://fasttrack.debian.net/debian bullseye-fasttrack InRelease
Invalid response from proxy: HTTP/1.0 500 Unable to connect Server: tinyproxy/1.10.0 Content-Type: text/html Connection: close [IP: 127.0.0.1 8082]
Err:2 tor+https://deb.whonix.org bullseye InRelease
Invalid response from proxy: HTTP/1.0 500 Unable to connect Server: tinyproxy/1.10.0 Content-Type: text/html Connection: close [IP: 127.0.0.1 8082]
Err:3 https://deb.qubes-os.org/r4.2/vm bullseye InRelease
Invalid response from proxy: HTTP/1.0 500 Unable to connect Server: tinyproxy/1.10.0 Content-Type: text/html Connection: close [IP: 127.0.0.1 8082]
Ign:8 tor+https://deb.debian.org/debian bullseye-backports InRelease
Err:5 tor+https://deb.kicksecure.com bullseye InRelease
Invalid response from proxy: HTTP/1.0 500 Unable to connect Server: tinyproxy/1.10.0 Content-Type: text/html Connection: close [IP: 127.0.0.1 8082]
Ign:4 tor+https://deb.debian.org/debian bullseye InRelease
Ign:6 tor+https://deb.debian.org/debian bullseye-updates InRelease
Ign:7 tor+https://deb.debian.org/debian-security bullseye-security InRelease
Ign:8 tor+https://deb.debian.org/debian bullseye-backports InRelease
Ign:4 tor+https://deb.debian.org/debian bullseye InRelease
Ign:6 tor+https://deb.debian.org/debian bullseye-updates InRelease
Ign:7 tor+https://deb.debian.org/debian-security bullseye-security InRelease
Ign:8 tor+https://deb.debian.org/debian bullseye-backports InRelease
Err:4 tor+https://deb.debian.org/debian bullseye InRelease
Invalid response from proxy: HTTP/1.0 500 Unable to connect Server: tinyproxy/1.10.0 Content-Type: text/html Connection: close [IP: 127.0.0.1 8082]
Err:6 tor+https://deb.debian.org/debian bullseye-updates InRelease
Invalid response from proxy: HTTP/1.0 500 Unable to connect Server: tinyproxy/1.10.0 Content-Type: text/html Connection: close [IP: 127.0.0.1 8082]
Err:7 tor+https://deb.debian.org/debian-security bullseye-security InRelease
Invalid response from proxy: HTTP/1.0 500 Unable to connect Server: tinyproxy/1.10.0 Content-Type: text/html Connection: close [IP: 127.0.0.1 8082]
Err:8 tor+https://deb.debian.org/debian bullseye-backports InRelease
Invalid response from proxy: HTTP/1.0 500 Unable to connect Server: tinyproxy/1.10.0 Content-Type: text/html Connection: close [IP: 127.0.0.1 8082]
Reading package lists... Done
E: Failed to fetch tor+https://deb.debian.org/debian/dists/bullseye/InRelease Invalid response from proxy: HTTP/1.0 500 Unable to connect Server: tinyproxy/1.10.0 Content-Type: text/html Connection: close [IP: 127.0.0.1 8082]
E: Failed to fetch tor+https://deb.debian.org/debian/dists/bullseye-updates/InRelease Invalid response from proxy: HTTP/1.0 500 Unable to connect Server: tinyproxy/1.10.0 Content-Type: text/html Connection: close [IP: 127.0.0.1 8082]
E: Failed to fetch tor+https://deb.debian.org/debian-security/dists/bullseye-security/InRelease Invalid response from proxy: HTTP/1.0 500 Unable to connect Server: tinyproxy/1.10.0 Content-Type: text/html Connection: close [IP: 127.0.0.1 8082]
E: Failed to fetch tor+https://deb.debian.org/debian/dists/bullseye-backports/InRelease Invalid response from proxy: HTTP/1.0 500 Unable to connect Server: tinyproxy/1.10.0 Content-Type: text/html Connection: close [IP: 127.0.0.1 8082]
E: Failed to fetch tor+https://fasttrack.debian.net/debian/dists/bullseye-fasttrack/InRelease Invalid response from proxy: HTTP/1.0 500 Unable to connect Server: tinyproxy/1.10.0 Content-Type: text/html Connection: close [IP: 127.0.0.1 8082]
E: Failed to fetch tor+https://deb.kicksecure.com/dists/bullseye/InRelease Invalid response from proxy: HTTP/1.0 500 Unable to connect Server: tinyproxy/1.10.0 Content-Type: text/html Connection: close [IP: 127.0.0.1 8082]
E: Failed to fetch tor+https://deb.whonix.org/dists/bullseye/InRelease Invalid response from proxy: HTTP/1.0 500 Unable to connect Server: tinyproxy/1.10.0 Content-Type: text/html Connection: close [IP: 127.0.0.1 8082]
E: Failed to fetch https://deb.qubes-os.org/r4.2/vm/dists/bullseye/InRelease Invalid response from proxy: HTTP/1.0 500 Unable to connect Server: tinyproxy/1.10.0 Content-Type: text/html Connection: close [IP: 127.0.0.1 8082]
E: Some index files failed to download. They have been ignored, or old ones used instead.
And the journal says:
May 02 14:56:01 host sudo[1245]: user : TTY=pts/0 ; PWD=/home/user ; USER=root ; COMMAND=/usr/bin/apt update
May 02 14:56:01 host sudo[1245]: pam_unix(sudo:session): session opened for user root(uid=0) by (uid=1000)
May 02 14:56:01 host systemd[1]: Started Forward connection to updates proxy over Qubes RPC (127.0.0.1:43396).
May 02 14:56:01 host systemd[1]: Started Forward connection to updates proxy over Qubes RPC (127.0.0.1:43408).
May 02 14:56:01 host systemd[1]: Started Forward connection to updates proxy over Qubes RPC (127.0.0.1:43418).
May 02 14:56:01 host systemd[1]: Started Forward connection to updates proxy over Qubes RPC (127.0.0.1:43420).
May 02 14:56:01 host systemd[1]: Started Forward connection to updates proxy over Qubes RPC (127.0.0.1:43434).
May 02 14:56:02 host systemd[1]: qubes-updates-proxy-forwarder@46-127.0.0.1:8082-127.0.0.1:43396.service: Succeeded.
May 02 14:56:02 host systemd[1]: Started Forward connection to updates proxy over Qubes RPC (127.0.0.1:43438).
May 02 14:56:02 host systemd[1]: qubes-updates-proxy-forwarder@47-127.0.0.1:8082-127.0.0.1:43408.service: Succeeded.
May 02 14:56:02 host systemd[1]: Started Forward connection to updates proxy over Qubes RPC (127.0.0.1:43450).
May 02 14:56:02 host systemd[1]: qubes-updates-proxy-forwarder@49-127.0.0.1:8082-127.0.0.1:43420.service: Succeeded.
May 02 14:56:02 host systemd[1]: Started Forward connection to updates proxy over Qubes RPC (127.0.0.1:43454).
May 02 14:56:03 host systemd[1]: qubes-updates-proxy-forwarder@48-127.0.0.1:8082-127.0.0.1:43418.service: Succeeded.
May 02 14:56:03 host systemd[1]: qubes-updates-proxy-forwarder@50-127.0.0.1:8082-127.0.0.1:43434.service: Succeeded.
......
Dom0 journal says:
dom0 qrexec-policy-daemon[2901]: qrexec: qubes.UpdatesProxy+: whonix-ws-16 -> @default: allowed to sys-whonix